Commercially available coloring solutions typically comprise water, metal cations selected from rare earth elements, transition metal and mixtures thereof, optionally complexing agent(s) and/or further additives like (poly)ethylene glycol. The coloring solutions are typically used for homogeneously coloring of porous dental ceramics. The coloring solutions are applied to the dental ceramic being in a porous and absorbent stage. After sintering, the dental ceramic usually shows a tooth-like color and is ready for veneering.
WO 2004/110959 (3M) relates to a coloring solution for ceramic framework. The solution comprises a solvent (e.g. water), a metal salt and polyethylene glycol having a Mn in the range of 1,000 to 200,000.
WO 00/46168 A1 (3M), corresponding to U.S. Pat. No. 6,709,694 B1 refers to coloring ceramics by way of ionic or complex-containing solutions containing defined concentrations of at least one salts or complexes of the rare earth elements or of the elements of the subgroups. The solution might contain additives like stabilizers, complex builders, pigments and beating additives.
WO 2008/098157 (3M) relates to a coloring solution for dental ceramic framework comprising a solvent, a coloring agent comprising metal ions, and a complexing agent, wherein the amount of complexing agent is sufficient to dissolve the coloring agent in the solvent.
WO 2009/014903 (3M) relates to a coloring solution for dental ceramic articles, the solution comprising a solvent and a coloring agent comprising rare earth element ions being present in the solution in an amount of at least about 0.05 mol/l solvent and transition ions being present in the solution in an amount of about 0.00001 to about 0.05 mol/l solvent.
WO 2010/062541 (3M) relates to a dental ceramic article comprising zirconium oxide and at least two different coloring substances showing light emission in the range of about 470 nm to 510 nm and light absorption in the range from about 520 nm to about 750 nm.
WO 2011/146761 (3M) relates to a dental article comprising two sections A and B, section A comprising zirconia in a certain amount and Dy, Sm, Eu or a mixture thereof, section B comprising a glass, glass ceramic or composite material.
WO 2013/022612 (3M) describes coloring solutions for selectively treating the surface of dental ceramic and related methods. The solution may comprise a solvent being miscible with water but not being water, an effect agent comprising metal ions, the effect caused by the effect agent being either coloring, providing fluorescence or a combination thereof, and a complexing agent being able to form a complex with the metal ions of the effect agent, wherein the complex is soluble in the solvent.
WO 2012/125885 (3M) relates to a dental ceramic article, process of production and use thereof. The dental ceramic article comprises ceramic components, the ceramic components comprising ZrO2 and Al2O3 and at least one component comprising Mn, Er or mixtures thereof. Described is also a kit of parts comprising a ceramic article and a coloring solution and process for producing a dental ceramic article. The content of these references is herewith incorporated by reference.
However, there is still room for improvement especially with regard to the requirements to be fulfilled with respect to modern dental materials. Patients and dentists nowadays have an increasing demand for highly aesthetic dental restorations.